In　recent　years,　the　ever-increasing　demand　for　networking　resources　and　energy,　fueled　by　the　unprecedented　upsurge　in　Internet　traffic,　has　been　a　cause　for　concern　for　many　service　providers.　Content　caching,　which　serves　user　requests　locally,　is　deemed　to　be　an　enabling　technology　in　addressing　the　challenges　offered　by　the　phenomenal　growth　in　Internet　traffic.　Conventionally,　content　caching　is　considered　as　a　viable　solution　to　alleviate　the　backhaul　pressure.　However,　recently,　many　studies　have　reported　energy　cost　reductions　contributed　by　content　caching　in　cache-equipped　networks.　The　hypothesis　is　that　caching　shortens　content　delivery　distance　and　eventually　achieves　significant　reduction　in　transmission　energy　consumption.　This　has　motivated　us　to　conduct　this　study　and　in　this　article,　a　comprehensive　survey　of　the　state-of-the-art　green　caching　techniques　is　provided.　This　review　paper　extensively　discusses　contributions　of　the　existing　studies　on　green　caching.　In　addition,　the　study　explores　different　cache-equipped　network　types,　solution　methods,　and　application　scenarios.　We　categorically　present　that　the　optimal　selection　of　the　caching　nodes,　smart　resource　management,　popular　content　selection,　and　renewable　energy　integration　can　substantially　improve　energy　efficiency　of　the　cache-equipped　systems.　In　addition,　based　on　the　comprehensive　analysis,　we　also　highlight　some　potential　research　ideas　relevant　to　green　content　caching.